1. Field of the Invention
The invention relates generally to network switches.
2. Background Art
A network switch is a device that provides a switching function (i.e., determines a physical path) in a data communications network. Switching involves transferring information, such as digital data packets or frames, among entities of the network. Typically, a switch is a computer having a plurality of circuit cards coupled to a backplane. In the switching art, the circuit cards are typically called “blades.” The blades are interconnected by a “switch fabric.” Each blade includes a number of physical ports that couple the switch to the other network entities over various types of media, such as Ethernet, FDDI (Fiber Distributed Data Interface), or token ring connections. A network entity includes any device that transmits and/or receives data packets over such media.
The switching function provided by the switch typically includes receiving data at a source port from a network entity and transferring the data to a destination port. The source and destination ports may be located on the same or different blades. In the case of “local” switching, the source and destination ports are on the same blade. Otherwise, the source and destination ports are on different blades and switching requires that the data be transferred through the switch fabric from the source blade to the destination blade. In some case, the data may be provided to a plurality of destination ports of the switch. This is known as a multicast data transfer.
Switches operate by examining the header information that accompanies data in the data frame. The header information includes the international standards organization (ISO) 7-layer OSI (open-systems interconnection model). In the OSI model, switches generally route data frames based on the lower level protocols such as Layer 2 or Layer 3. In contrast, routers generally route based on the higher level protocols and by determining the physical path of a data frame based on table look-ups or other configured forwarding or management routines to determine the physical path (i.e., route).
Ethernet is a widely used lower-layer network protocol that uses broadcast technology. The Ethernet frame has six fields. These fields include a preamble, a destination address, source address, type, data and a frame check sequence. In the case of an ethernet frame, the digital switch will determine the physical path of the frame based on the source and destination addresses. Standard Ethernet operates at a ten Mbit/s data rate. Another implementation of Ethernet known as “Fast Ethernet” (FE) has a data rate of 100 Megabits/s. Yet another implementation of FE operates at 10 Gigabits/sec.
A digital switch will typically have physical ports that are configured to communicate using different protocols at different data rates. For example, a blade within a switch may have certain ports that are 10 Mbit/s, or 100 Mbit/s ports. It may have other ports that conform to optical standards such as SONET and are capable of such data rates as 10 gigabits per second.
A performance of a digital switch is often assessed based on metrics such as the number of physical ports that are present, and the total bandwidth or number of bits per second that can be switched without blocking or slowing the data traffic. A limiting factor in the bit carrying capacity of many switches is the switch fabric. For example, one conventional switch fabric was limited to 8 gigabits per second per blade. In an eight blade example, this equates to 64 gigabits per second of traffic. It is possible to increase the data rate of a particular blade to greater than 8 gigabits per second. However, the switch fabric would be unable to handle the increased traffic.
It is desired to take advantage of new optical technologies and increase port densities and data rates on blades. However, what is needed is a switch and a switch fabric capable of handling higher bit rates and providing a maximum aggregate bit carrying capacity well in excess of conventional switches.